Genetic diversity of kochia was determined using 45 polymorphic intersimple sequence repeat markers. Comparisons of genetic diversity within and among populations were made after structuring 453 kochia plants into samples representing 13 populations on the basis of the collection site and into two sample groups on the basis of the cropping history and geographic region of the sites. Mean Nei's gene diversity (h) for the 13 populations was 0.35, and total diversity (HT) was 0.35, indicating that genetic diversity in kochia is very high. There was a greater proportion of diversity within (HS = 0.31) populations than among (GST = 0.09) populations. A hierarchical analysis of molecular variance showed that 90% of the variation occurred within populations (P = 0.0001). Of the remaining variance, 4.5% was attributed to differences between the two groups (P = 0.0001) and 5.5% to differences among the 13 populations within the groups (P = 0.0001). Gene flow (Nm) among populations was 2.4. The high level of gene diversity and large proportion of within-population diversity in kochia suggest that, despite generations of herbicide selection, kochia maintains high genetic diversity through substantial levels of gene flow within and among populations.
Nomenclature: Kochia, Kochia scoparia (L.) Schrad. KCHSC.